1. Field of the Invention
The present invention relates to an improved yeast extract for use in the cosmetic arts, which maintains the cell-stimulatory effects of the prior art yeast extracts, while providing additional photo-protective effects.
2. Description of the Prior Art
The aging process is accompanied by the slowing of physiologic life processes. Foremost among these is the decrease in the body""s ability to maintain a hemostatic environment when faced with a chronic, daily onslaught of stresses. Aging results in part from damage to cells and tissues by a variety of factors both internal and external, natural and artificial. Our bodies have evolved genetically to recognize these damages and instigate their repair, and in some cases degrade the resulting abnormal proteins. The affects of the aging progression become evident in our skin.
Yeast, because its processes closely resemble those of individual human cells, has become a mainstay of biochemical research. Its genome completely defined, yeast is an ideal tool with which to study cellular defense mechanisms. Man has commercially harnessed the production capacity of yeast to produce a variety of pharmaceutical and cosmetic active ingredients. Within the cosmetic industry, one driving force for harnessing yeast has been the movement away from animal-derived active ingredients for ethical, regulatory or safety concerns.
Cellular damage provokes defensive responses from cells. Exposure to heat, UV radiation, pollutants or other adverse conditions stimulates the generation of defensive gene products. These defensive gene products can promote cell respiration, cell proliferation or cell viability in the face of adverse conditions.
George Sperti found that yeast cells could be stimulated by heat, UV radiation, x-rays or chemical injury to produce stress-induced defensive factors, later termed xe2x80x9cheat shock proteinsxe2x80x9d. These heat shock proteins (Hsp) might be more appropriately called xe2x80x9cstress response proteinsxe2x80x9d. Sperti""s research has shown that yeast, rat, mouse, chick and various bacterial cells all produce stress factors upon injury that could stimulate cellular repair in cultured cells derived from other species. See U.S. Pat. No. 2,239,345. Heat shock proteins either replace cellular functions disabled by the stress or act as molecular chaperones protecting native structures typically by modifying protein folding.
Viable yeast cultures exposed to UV light of a specified wavelength (286 nm) produce the isolate known as Live Yeast Cell Derivative (LYCD). LYCD has seen broad application within the pharmaceutical and cosmetic industries. Whitehall Labs has used LYCD as a wound-healing agent in their anti-hemorrhoidal preparations. Studies have shown that LYCD will increase the rate of wound healing in humans where the wounds were a result of either thermal or mechanical damage. See Goodson, et al., Augmentation of some aspects of wound healing by xe2x80x9cskin respiratory factorxe2x80x9d. J. Surg. Res. (1976) 21. 125-129. The rate of wound healing is associated with an increase in collagen synthesis, which is believed to be associated with elevated fibroblast respiration.
The ability of LYCD to promote fibroblast activity has accounted for its popular use in cosmetics. Several U.S. patents revolve around the use of LYCD for moisturizing or improving skin""s appearance. See, for instance, U.S. Pat. No. 5,643,587 or 5,676,956 or 5,776,441. It is thought that by increasing collagen and elastin synthesis, LYCD acts as an internal moisturizer binding water in the skin. Cosmetic application of LYCD increases oxygen uptake by cells and stimulates repair, in turn slowing visible signs of aging. LYCD is capable of preventing the accumulation of stress-damaged proteins in the sells and in the body by initiating their breakdown.
It has often been discussed that oxygen is a xe2x80x9cdangerous friendxe2x80x9d. Oxidation is one of the major mechanisms of aging, both intrinsic and extrinsic. Yeast possesses the same mechanism for combating oxidative stress as higher eukaryotes, containing distinct transcriptional activators which respond to hydrogen peroxide and superoxide anions. J. Gen. Microbiol. 139 501-507. Recent work has identified over 100 proteins that are stimulated by sub-lethal doses of hydrogen peroxide. J Biol. Chem. (1998) 273(34) 2280-2289.
It is therefore an object of the present invention to provide a yeast cell extract for use in the cosmetic arts which provides the same or better cell stimulatory effects of the prior art while providing new protection from cellular damage caused by activated oxygen species and/or UV light.
It is a further object of the present invention to provide a cosmetic composition with properties of cell stimulation and protection from cellular damage caused by activated oxygen species and/or UV light.
It is yet another object of the present invention to provide a method of preparing a yeast cell extract which has the properties of cell stimulation and protection from cellular damage caused by activated oxygen species and/or UV light.
These objects are achieved by a process of and product resulting from adding a sub-lethal amount of a peroxide to a growing culture of yeast, observing the change in absorbance of the culture at 256 nm as a measure of the injury occurring to the yeast cells, and, upon reaching a predetermined absorbance value, purifying the water-soluble yeast extract from the peroxide containing yeast culture. The resulting product has at least 1.5 respiratory units per mg dry weight and has significantly increased amounts of 15, 25 and 55 kD molecular weight products compared to a Live Yeast Cell Derivative as determined by SDS slab gel electrophoresis. This product can be combined with a cosmetically acceptable carrier to provide a composition suitable for topical application to the skin.
As used herein, xe2x80x9crespiratory unitxe2x80x9d is defined as the quantity of PTYE which increases oxygen consumption of 1 mg of rat abdominal tissue by 1% in a one hour period when measured by Warburg manometry.
As used herein, xe2x80x9ccosmetically acceptable carrierxe2x80x9d includes those carriers known for use in lotions, creams, toners or masks for skincare, those carriers known for use in decorative products such as lipsticks, concealers, foundations or powders and those caries known for use in leave-in haircare preparations such as tonics, gels and lotions. The yeast extracts of the instant invention can be used to replace LYCD in any cosmetic formulation.
As used herein, xe2x80x9csub-lethal amountxe2x80x9d means an amount that provides a kill rate of less than 90% of the viable cells. A minimum effective concentration of the peroxide is one which produes measurable increase in absorbance of the culture of light having a wavelength of 256 nm.
As used herein, xe2x80x9cperoxidexe2x80x9d means any chemical compound containing a peroxide group. Furthermore, an embodiment of the invention uses in place of the peroxide nonperoxide chemical compounds that provide oxidative stress. Oxidative stress is the damaging effects of oxidation caused by reactive oxygen species. Examples of nonperoxide chemical compounds that provide oxidative stress include superoxide anion, hydroxyl radical and nitric oxide.